Intervertebral prosthesis

ABSTRACT

An intervertebral prosthesis for insertion between adjacent vertebrae includes upper and lower prosthesis plates locatable against respective vertebrae and having opposing, concavely curved recesses therein, and a core located between the plates. The core has opposed, convexly curved surfaces received in the recesses of the plates to allow the plates to slide in articulated manner over the core. The opposed surfaces of the core and the recesses of the plates have cooperating spherical curvatures. The recess of each plate surrounds a locating peg projecting centrally from the base of the recess and is bounded by an annular rim, such that the annular rims of the plates are arranged to contact one another at a predetermined limit of sliding movement of the plates over the core. The peg locates loosely in an opening located centrally in a curved surface of the core, whereby the plates can slide over the core in all directions while the peg holds the core captive.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 15/458,913 (Attorney Docket No. 29850-710.306), filed Mar. 14, 2017,now U.S. Pat. No. ______, which is a continuation of U.S. patentapplication Ser. No. 15/284,344 (Attorney Docket No. 29850-710.305),filed Oct. 3, 2016, which is a continuation of U.S. patent applicationSer. No. 11/982,420 (Attorney Docket No. 29850-710.304), filed Oct. 31,2007, which is a continuation of Ser. No. 11/084,224 (Attorney DocketNo. 29850-710.501) filed Mar. 18, 2005, now U.S. Pat. No. 7,531,001,which is a continuation-in-part of PCT/IB2003/001529 (Attorney DocketNo. 29850-710.601) filed on Apr. 24, 2003, designating the UnitedStates, which claimed priority from South African application 2002/7517filed on Sep. 19, 2002, the full disclosures of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an intervertebral prosthesis.

In the event of damage to a spinal disc it is known practice to implantan intervertebral prosthesis surgically to replace the damaged organ.Several types of prosthesis for this purpose are known and in commonuse.

One type of known intervertebral prosthesis is sold by Waldemar LinkGmbH & Co under the trade mark LINK® SB Charite. This prosthesisincludes upper and lower prosthesis plates which locate against andengage the adjacent vertebral bodies, and a low friction core betweenthe plates. The core has upper and lower convexly curved surfaces andthe plates have corresponding, concavely curved recesses which cooperatewith the curved surfaces of the core. This allows the plates to slideover the core to allow required spinal movements to take place. Thecurved recesses in the plates are surrounded by annular ridges whichlocate, at the limit of sliding movement of the plates over the core, inopposing peripheral channels surrounding the curved surfaces of thecore.

This type of configuration is also described in EP 0 560 140 and EP 0560 141 (both Waldemar Link GmbH & Co). However a drawback of suchconfigurations is that the provision of the peripheral ribs and channelslimits the areas available for bearing and sliding contact between theplates and core, and accordingly the loads which can be transmitted bythe prosthesis. As a result of the relatively small bearing areas, it isbelieved that at least the core will be subject to rapid wear and have arelatively short life-span.

EP 0 560 141 also describes one alternative arrangement in which thecurved surfaces of the core carry opposing, elongate keys that locate inelongate grooves in the plates and another alternative arrangement inwhich the plates have opposing elongate keys that locate in elongategrooves in the opposite curved surfaces of the core. These key andgroove arrangements allow the plates to slide freely over the core,within the limits of the length of the grooves, in one plane only.Although allowance is made for some lateral play of the keys in thegrooves, very little sliding movement of the plates over the core cantake place in the orthogonal vertical plane, and this is considered tobe a serious drawback of this design.

2. Description of the Background Art

European Patent Publications EP 0 560 140 and EO 0 560 141 have beendiscussed above. U.S. Patent Publications US2002/0035400 andUS2002/0128715 describe intervertebral prostheses with center-postsreceived in passages in a core. The core possesses an annular flangestructure engaged by extensions on the plates.

BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided an intervertebralprosthesis for insertion between adjacent vertebrae, the prosthesiscomprising upper and lower prosthesis plates locatable against therespective vertebrae and having opposing, concavely curved recessestherein and a core located between the plates, the core having opposed,convexly curved surfaces received in the recesses of the plates to allowthe plates to slide in articulated manner over the core, characterizedin that:

-   -   the opposed surfaces of the core and the recesses of the plates        have cooperating spherical curvatures,    -   the recess of a plate surrounds a locating peg projecting        centrally from the base of the recess, and    -   the peg locates loosely in an opening located centrally in a        curved surface of the core, whereby the plates can slide over        the core in all directions while the peg holds the core captive.

In some embodiments, only one of the plates, typically the operativelylower plate, includes a peg. In other embodiments, both plates includepegs, the pegs opposing one another and locating loosely in respectiveopenings located centrally in the opposed curved surfaces of the core.In each embodiment it is preferred that each peg and the opening inwhich it locates are conical in shape.

According to another aspect of the invention there is provided aprosthesis plate for use in a prosthesis as summarized above, theprosthesis plate having a coarse surface locatable against a vertebra,an oppositely facing concavely curved surface which is complemental inshape to a convexly curved surface of a core of the prosthesis,characterized in the concavely curved surface of the plate has aspherical curvature and in that the plate includes a conical locatingpeg extending centrally from the concavely curved surface, the peg beinglocatable loosely in a central opening in the convexly curved surface ofthe core.

According to yet another aspect of the invention there is provided acore for use in the prosthesis, the core comprising a one piece plasticsbody having operatively upper and lower curved surfaces, characterizedin that the curved surfaces of the body are spherically curved and atleast one of the surfaces has a central, conical opening thereindimensioned to receive a conical locating peg of a prosthesis plateloosely.

Other features of the invention are set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a cross-sectional view of a prosthesis plate used in aprosthesis according to the invention;

FIG. 2 shows a plan view of the prosthesis plate seen in FIG. 1;

FIG. 3 shows a cross-sectional view of a core used in a prosthesisaccording to the invention;

FIG. 4 shows a plan view of the core seen in FIG. 3;

FIG. 5 shows a cross-sectional view of an intervertebral prosthesisaccording to a first embodiment of the invention in a neutral conditionbefore articulation has taken place;

FIG. 6 shows the prosthesis of FIG. 5 articulated to a limit position;and

FIG. 7 shows a cross-sectional view of an intervertebral prosthesisaccording to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The prosthesis plate 10 seen in FIGS. 1 and 2 may be formed fromtitanium, typically being formed in one piece of grade 5 titanium. Othersuitable materials include titanium nitrides, cobalt chrome alloys, andceramics. The prosthesis plate includes a major surface 12 which ismachined to a coarse, serrated finish 14. Projecting from the surface 12is an elongate fin 16 pierced by transverse holes 18. The oppositesurface of the plate 10 is formed with a recess 20 surrounding aprojecting conical peg 22 of round cross-section at the center of therecess. The recess is bounded by an annular rim 24. The surface 26 ofthe recess is concavely, spherically curved and has a titanium nitridefinish.

A first embodiment of prosthesis of the invention, indicated generally,by the numeral 28 in FIGS. 5 and 6, includes a pair of identicalprosthesis plates 10 arranged in opposition to one another. Theprosthesis 28 also includes a core 30 illustrated in FIGS. 3 and 4. Thecore is made in one piece of a low friction plastics material, in thiscase a polyethylene known as Orthosol, but a variety of other highmolecular weight polyethylenes might also find use. Alternatively, thecore could be composed of a metal, such as cobalt chrome, or of aceramic. The core is generally in the form of a circular,doughnut-shaped toroid and has identical upper and lower surfaces 32which are convexly, spherically curved. The upper and lower surfaces 32are formed centrally with conical openings 34, in this case forming theopposite ends of a circular cross-section passage 36 passing axially andcentrally through the body of the core.

The core surfaces 32 and recess surface 26 have the same radius ofcurvature which is, in this case, 18 mm.

In the assembled prosthesis 28, the plates 10 are arranged in oppositionto one another with the core 30 located between them. The pegs 22 of theplates locate in the openings 34, i.e. in the ends of the passage 36.The combined length of the pegs is less than the length of the passage36, so the inner ends of the pegs are spaced apart from one another by ashort distance 38, as shown in FIG. 5. The transverse dimension of eachpeg is, at all points along the length of the peg, considerably lessthan the diameter of the passage 36 at the corresponding point along thelength of the passage.

The cooperating spherical surfaces 26 and 32 and the relative dimensionsof the pegs 22 and the passage 36 allow the plates 10 to slide orarticulate over the core through a fairly large range of angles and inall directions or degrees of freedom, including rotation about thecentral axis.

At a predetermined limit of articulated movement of the plates relativeto the core, the rims 24 of the plates contact with one another asindicated by the numeral 40 in FIG. 6. Further articulation of theprosthesis 28 beyond this point is not possible. At the limit ofarticulation, the pegs 22 also come into abutment with the side of thepassage 36, as also illustrated in FIG. 6.

It will also be noted in FIG. 6 that the openings 34 at the ends of thepassage 36 are defined by similar cone angles to the pegs 22, so thatcontact between the pegs and the sides of the openings takes placecomplementally over virtually the entire length of each peg.

Throughout the range of possible articulation, the pegs 22 remain in thepassage 36 and prevent the core from separating laterally from theplates 10. In other words, the core is held captive by the pegs duringall possible articulations which can take place. In the illustratedembodiment, the plates 10 are limited to 12° of articulation before therims 24 abut one another, i.e. 12° is the maximum articulation which cantake place.

In the prosthesis 28 described above, the pegs 22 locate in a passage 32which passes right through the core 30. It will however be understoodthat in other embodiments, the pegs could merely locate in blindrecesses or openings in the opposite surfaces of the core without suchopenings actually being joined to one another to form a continuouspassage.

FIG. 7 illustrates a prosthesis according to a second embodiment of theinvention in a view similar to that of FIG. 5. In FIG. 7, componentscorresponding to components illustrated in the earlier Figures areindicated by the same reference numerals.

The lower prosthesis plate 10 in FIG. 7 is identical to the prosthesisplates of the first embodiment. However, the upper prosthesis plate,designated 10.1, has no central peg. Instead, the surface 26 iscontinuously, spherically curved. In all other respects the plate 10.1is identical to the plate 10.

In the assembled prosthesis 50, the core is held captive by the actionof the single peg 22 carried by the lower prosthesis plate 10. The core30 is identical to the core described previously but once again it willbe appreciated that core could have a blind recess in its downwardlyfacing, curved surface 32 only to receive the single peg 22.

The prosthesis 28, 50 is surgically implanted between adjacent spinalvertebrae in place of a damaged disc. Those skilled in the art willunderstand that the adjacent vertebrae are forcibly separated from oneanother to provide the necessary space for insertion. The plates 10,10.1 are slipped laterally into place between the vertebrae with theirfins 16 entering slots cut in the opposing vertebral surfaces to receivethem.

After insertion of the core between the opposing plates, the vertebraare allowed to move together to hold the assembled prosthesis in place.

The surfaces 12 of the plates 10, 10.1 locate against the opposingvertebrae and, with passage of time, firm connection between the platesand the vertebrae will be achieved as bone tissue grows over theserrated finish. Bone tissue growth will also take place about the fins16 and through the holes 18 therein, further enhancing the connectionwhich is achieved.

Referring to FIGS. 3 and 4, the core 30 used in the embodimentsdescribed above is formed with narrow, angularly spaced, blind passageswhich accommodate titanium pins 42. The core itself is transparent toX-radiation and so would normally be invisible in a post-operative X-rayexamination. The pins 42 serve as radiographic markers and enable theposition of the core 30 to be ascertained during such examination.

Annular grooves 44 are provided in the plates 10, 10.1 to facilitateholding and manipulation of the prosthesis by appropriate instrumentsduring placement into the intervertebral disc space.

Compared to known prostheses, the prostheses 28, 50 described above havea number of advantages, as follows:

1. The peg or pegs 22 hold the core captive and prevent it from slippingout sideways.

2. At a predetermined maximum limit of articulation, the rims 24 contactone another to prevent further articulation. At the same time, the pegor pegs 22 contact the sides of the openings 34, also preventing furtherarticulation.

3. An acceptable bearing area of the plates on the core is obtained withthe central peg/central opening configurations described above. This isparticularly advantageous compared to prior art prostheses where thecore has peripheral channels on its upper and lower surfaces to receiveperipheral rims on the plates at the limit of articulation.

In practice, it may happen that there is imperfect alignment of theprosthesis plates. In the case of very poor alignment, the dual pegconfiguration of FIGS. 5 and 6 gives rise to the possibility that thepegs 22 are laterally offset from one another by a substantial distance.This can in turn lead to the undesirable consequence that the range ofarticulation which can be accommodated is unduly limited, and attemptsto articulate past the limit could result in damage to the core by themisaligned pegs. In the embodiment of FIG. 7 the single peg can bereceived centrally by the core, thereby avoiding this potential problem.

The principles of the invention are applicable to prosthetic discimplants for lumbar vertebrae as well as cervical vertebrae. In thelatter case, the fins 16 will typically be omitted.

What is claimed is:
 1. A method of inserting an intervertebralprosthesis in an intervertebral space, the method comprising: providingan articulating intervertebral prosthesis including: a first prosthesisplate having a major surface to engage the first vertebra and acooperating surface disposed opposite the major surface; a secondprosthesis plate comprising a major surface to engage the secondvertebra and a cooperating surface disposed opposite the major surface;a core located between the first and second plates, wherein thecooperating surfaces of the first and second plates are arranged tocooperate with the core to form an articulate joint; a peg projectingcentrally from the cooperating surface of the first plate and a centralopening in the core, wherein the peg locates loosely in the opening ofthe core, whereby the plates can slide over the core while the peg holdsthe core captive and wherein the second plate does not include a centralprojecting peg; wherein the core includes at least one continuouslycurved bearing surface; a first annular rim disposed around thecooperating surface of the first plate, the first rim having an emptygroove formed adjacent to the first rim; a second annular rim disposedaround the cooperating surface of the second plate, the second rimhaving an empty groove formed adjacent to the second rim; and eachgroove configured and arranged to facilitate handling of the plates byinstruments used to place the prosthesis in use; and manipulating theprosthesis with an instrument to place the prosthesis in entirely withinthe intervertebral space; wherein the grooves facilitate manipulationand holding of the prosthesis while the prosthesis is placed in theintervertebral space.
 2. The method according to claim 1, wherein thefirst and second prosthesis plates are secured to vertebrae adjacent theintervertebral space by elongated protrusions extending from the majorsurfaces of the first and second plates.
 3. The method according toclaim 1, wherein the second plate does not include a central projectingpeg.
 4. An intervertebral prosthesis for insertion between adjacentvertebrae, the prosthesis comprising: first and second prosthesis plateslocatable against respective vertebrae, each of the first and secondprosthesis plates having an outer surface locatable against a vertebraand an oppositely facing inner bearing surface; at least one upstandingelongated protrusion the outer surface of each of the first and secondprosthesis plates; a core located between the plates, the core having aheight extending between the plates which is smaller than a width of thecore in a direction perpendicular to the height, the core havingopposed, first and second bearing surfaces configured to allow theplates to slide in an articulated manner over the core; a peg projectingcentrally from the inner bearing surface of the first plate; wherein thepeg locates loosely in an opening located centrally in a first bearingsurface of the core, whereby the first plate can slide over the corewhile the peg holds the core captive; wherein the second bearing surfaceof the core is continuously convexly curved with no central opening; andwherein each of the first and second plates are bounded by an annularrim, and wherein each plate includes a groove adjacent to the rim, eachgroove configured and arranged to facilitate handling of the plate byinstruments used to place the prosthesis in use.
 5. The prosthesisaccording to claim 4, wherein the peg and the opening in which itlocates are conically shaped.
 6. The prosthesis according to claim 4,wherein the inner bearing surface of the second plate is concave andcomplementary in shape to the convexly curved second bearing surface ofthe core.
 7. The prosthesis according to claim 4, wherein the core is adoughnut-shaped body and the central opening therein is provided by acentral passage extending axially through the body.
 8. The prosthesisaccording to claim 4, wherein the opening located centrally in the firstbearing surface of the core is a blind recess extending partway throughthe core.
 9. The prosthesis according to claim 4, wherein the peg isarranged to abut a side wall of the opening at a predetermined limit ofsliding movement of the plates over the core.
 10. The prosthesisaccording to claim 4, wherein the peg and opening are complementary inshape.
 11. The prosthesis according to claim 4, wherein the outersurfaces of the first and second prosthesis plates comprise coursefinishes.
 12. The prosthesis according to claim 4, wherein the first andsecond prosthesis plates are formed of titanium.
 13. The prosthesisaccording to claim 12, wherein the core is formed of high molecularweight polyethylene.
 14. The prosthesis according to claim 4, whereinduring articulation, the peg remains in the opening and the articulationof the prosthesis is limited to a maximum of 12° of articulation. 15.The prosthesis according to claim 4, wherein the first and secondprosthesis plates are each formed in one piece of titanium andconfigured to be received entirely within the disc space.
 16. A systemfor insertion of an intervertebral prosthesis between adjacentvertebrae, the system comprising: an intervertebral prosthesiscomprising: a first prosthesis plate having a major surface to engagethe first vertebra and a cooperating surface disposed opposite the majorsurface; a second prosthesis plate comprising a major surface to engagethe second vertebra and a cooperating surface disposed opposite themajor surface; a core located between the first and second plates,wherein the cooperating surfaces of the first and second plates arearranged to cooperate with the core to form an articulate joint; a pegprojecting centrally from the cooperating surface of the first plate anda central opening in the core, wherein the peg locates loosely in theopening of the core, whereby the plates can slide over the core whilethe peg holds the core captive and wherein the second plate does notinclude a central projecting peg; wherein the core includes at least onecontinuously curved bearing surface; a first annular rim disposed aroundthe cooperating surface of the first plate, the first rim having a firstgroove formed adjacent to the first rim; a second annular rim disposedaround the cooperating surface of the second plate, the second rimhaving a second groove formed adjacent to the second rim; and eachgroove configured and arranged to facilitate handling of the plates byinstruments used to place the prosthesis in use; and an instrument forplacing the intervertebral prosthesis, the instrument configured to holdthe prosthesis at the first and second grooves.
 17. The system accordingto claim 16, wherein the cooperating surface of the second plate iscurved and the core has a cooperating convexly curved surface.
 18. Thesystem according to claim 16, wherein the central opening in the core isa blind recess extending partway through the core.
 19. The systemaccording to claim 16, wherein the first and second prosthesis platesare each formed in one piece and configured to be received entirelywithin a disc space between the adjacent vertebrae.
 20. The systemaccording to claim 16, wherein the second plate does not include acentral projecting peg.